1. Technical Field
The present invention concerns a piston rings, and more particularly to the geometry of the piston ring.
2. Related Art
DE-C 39 20 449 shows a self-tightening, air-tight piston ring, the upper plane surface of which, in the installed position, is in contact with the piston's grooved plane surface from the mid-point of the latter's radius to its center. The piston ring's lower plane surface is sloped, relative to the piston's grooved surface, such that the latter, from the mid-point of its radius to its center, is likewise in contact with the piston ring. The cross-section of the inner circumferential surface shows a variation in the form of a bevel.
U.S. Pat. No. 2,591,920 shows a piston ring which is equipped with a variable configuration in its cross-section cut in the area of its inner circumferential surface.
A piston ring for internal combustion engines, which possesses varying wall thicknesses seen across its circumference, has become known through JP-A 09196171.
Piston rings available on today's market often plan for a twisting of the piston ring by maintaining a consistent angle across the cross-section cut (for example, the internal angle or bevel). This consistent cross-section working under the bending tension of installation causes an uneven twisting in the ring in accordance with piston ring design theory, regardless of the circumference.